1. The Field of the Invention
The present invention relates to pressure gauges for monitoring fluid pressure generated in a syringe during a medical procedure such as angioplasty. More particularly, the present invention relates pressure gauges that are isolated from potential sources of contamination so as to be repeatedly used in medical procedures without being sterilized between uses.
2. Relevant Technology
In recent years, balloon-tipped catheters have become increasingly useful in various medical procedures. For example, balloon-tipped catheters have been used to reduce the intrusiveness of medical procedures in various fields of medicine, such as urology, gynecology, cardiology, and the like. Particularly in the treatment of coronary artery disease, the use of balloon-tipped catheters and their associated fluid pressurization systems has become widespread.
Coronary artery disease is the narrowing of the arteries that feed oxygen-rich blood to the heart. The heart needs adequate amounts of oxygen to continually and efficiently pump blood throughout the body. When arteries leading to the heart become narrowed and constricted due to coronary artery disease, several problems can develop. A person with coronary artery disease can experience angina, which is characterized by chest pain or pressure that radiates to the aim or jaw and is caused by a lack of oxygen-rich blood to the heart muscle. If untreated, coronary artery disease can lead to or contribute to heart failure and death.
In recent years, coronary angioplasty has become a common and accepted alternative to the vastly more intrusive coronary bypass surgery. Coronary bypass surgery involves surgical access to the heart, placing the patient on an extracorporeal blood oxygenation system so that the heart can be stopped for surgery, and then surgically attaching one or more passageways by which blood can bypass a clogged coronary artery, all under general anesthesia. Coronary angioplasty, which can be performed using a local anesthetic, involves running a dilation or "balloon-type" catheter to the diseased artery and then inflating the balloon in order to compress plaque within the artery, thereby obtaining increased blood flow to the heart. Compared to coronary bypass surgery, coronary angioplasty is less intrusive and traumatic, typically involves less risk to the patient, and significantly reduces the patient's discomfort and recovery time.
During inflation of the balloon during angioplasty, no blood can flow through the artery that is being mechanically dilated. The disruption of blood flow must be limited in duration to about 20 to 60 seconds, so as to avoid tissue damage due to oxygen deprivation. Hence, it is important to carefully monitor the inflation pressure and duration to ensure that blood flow is restored before tissue damage can occur. In most cases, it is not possible to adequately dilate a diseased artery in a single inflation. In cases where it is necessary to undertake multiple inflations in the same artery, it is important to allow sufficient time between successive inflations so that the tissues fed by the diseased artery can become fully oxygenated before blood flow is disrupted again. At the same time, a successful angioplasty procedure requires that the dilation of the artery be conducted for a significant period of time.
Various devices and gauges have been developed for monitoring inflation and deflation of balloon tipped catheters during angioplasty. A typical pressure gauge of the prior art has a pressure transducer diaphragm that is in direct fluid contact with the inflation fluid within the inflation syringe. For example, the pressure gauge is directly mounted on the exterior of the syringe barrel over a port extending through the barrel. As fluid pressure is generated within the inflation syringe, the fluid pressure is transmitted through the port to the pressure transducer diaphragm. The pressure gauge senses the fluid pressure and displays or records the magnitude of the fluid pressure in analog or digital form.
In order to maintain a sterile environment during the angioplasty procedure, several techniques have been developed with respect to pressure gauges and methods of sensing fluid pressure. It can be understood that as the pressure transducer diaphragm is exposed to inflation fluid, the pressure gauge is subject to possible contamination. Moreover, the exposed surfaces of the pressure gauge, such as the housing and a display window through which the measurement readings are displayed, may be exposed to other contaminants during use. For example, medical personnel sometimes touch the pressure gauge during normal use and fluids may be splashed onto pressure gauge surfaces. Although pressure gauges and the inflation fluid ordinarily do not contact the patient's tissue or bodily fluids, it is important that the pressure gauges be sterile for safety reasons. Using a pressure gauge that has previously been contaminated by inflation fluid or contact with other contaminants without subjecting it to a sterilization procedure has been unacceptable according to current medical practice.
One method for providing sterile pressure gauges is to use a new device for each angioplasty or other medical procedure. According to this method, the pressure gauges are one-use devices that are discarded after one medical procedure. Disposable pressure gauges ensure that each angioplasty is performed with a sterile pressure gauge. However, the use of disposable pressure gauges adds significant cost to each operation.
Alternatively, other pressure gauges are designed to be sterilized after being used in a medical procedure, and are thereby reusable. For example, sterilization may be conducted thermally in an autoclave or chemically by applying a sterilizing chemistry to the pressure gauge. Typically, such sterilizable pressure gauges have surfaces of stainless steel or another sterilizable material. Examples of sterilizable and reusable pressure gauges are disclosed in copending U.S. patent application Ser. No. 09/048,091, filed Mar. 25, 1998, entitled "Pressure Gauge with Digital Stepping Motor and Reusable Transfer Plug." For purposes of disclosure, the foregoing patent application is incorporated herein by specific reference. Sterilizable pressure gauges represent a significant advancement in the art, since the cost of a new pressure gauge is not included in each medical procedure.
Either of the foregoing two methods are adequate for providing sterile pressure gauges in many situations. However, it can be understood that it would be a fixer advancement in the art to provide pressure gauges that are both reusable and do not need to be sterilized between uses. Pressure gauges that may be used multiple times without intervening sterilization procedures would significantly reduce the cost and effort now required for providing sterile pressure gauges. In particular, the cost associated with the time and equipment for sterilizing reusable pressure gauges could be avoided. In addition, such pressure gauges would eliminate the cost of using a new, one-use pressure gauge for each medical procedure.